Operation frequencies of information processing equipment such as network units or personal computer have been remarkably raised recently from megahertz to gigahertz. Thereby, a waveform analysis considering influences of various noises is requested also for a high-frequency signal for transmitting a wiring pattern of a printed circuit board.
A circuit designer of an integrated circuit and the like selects a circuit device constituting a circuit and a parameter for controlling the characteristic of the circuit device so that operations of the circuit are suited to a purposed specification before designing the circuit.
At the present when the computer art is developed, a circuit simulator is used for circuit design. The circuit simulator simulates a circuit operation on a computer without fabricating an actual circuit and shows the circuit operation for a designer. The simulator operated by the software referred to as SPICE2 developed by University of California at Berkley in 1972 is publicly known.
For example, in the case of an analysis using the above circuit simulator, a simulation is executed in accordance with the connection data between circuit devices constituting a circuit to be analyzed and device parameters to estimate the number of noises under a predetermined operational state of each circuit device and display or print the estimated number of noises.
Moreover, a random-pattern analysis has been performed so far, in which the waveform of a random pattern is falsely generated to analyze the reflection characteristic when the random pattern is transmitted to the circuit. As shown in FIG. 26A, the waveform of the random pattern shows a differential waveform constituted of a negative waveform 70 and a positive waveform 71.
Because the differential waveform makes it possible to cancel noises by using the difference between the negative waveform 70 and positive waveform 71 even if noises are superimposed on the negative waveform 70 and positive waveform 71, it is a waveform having a high noisiness. Moreover, the differential waveform is defined as bit 0 when the positive waveform 71 is equal to 0 V and bit 1 when the positive waveform 71 is equal to 3 V.
The above random pattern is obtained by combining the bit 1 and the bit 0 at random, in which the reflection characteristic is almost certainly deteriorated in the case of a specific combination. Therefore, by intentionally falsely transmitting a random pattern to the circuit, it is possible to determine good or bad of the reflection characteristic.
To generate the waveform of a random pattern by a conventional circuit simulator, it is necessary to carefully manually set rise and fall timings of the positive waveform 71 (Pos_Wave) and the negative waveform 70 (Neg_Wave) as shown in FIG. 26B.
As described above, the conventional circuit simulator shows the power in a waveform analysis up to approx. 100 MHz and is greatly supported by various designers. Because frequencies of information equipment have been remarkably raised recently and are reaching a gigahertz band from a megahertz band, a waveform analysis considering influences of various noises is requested for a high-frequency signal for transmitting a wiring pattern to a printed circuit board.
However, the conventional circuit simulator has a problem that it is not easy to correspond to signal analyses such as the skew analysis, jitter analysis, and eye-pattern analysis of a high-frequency differential signal and a general signal.
Moreover, as described by referring to FIG. 26A and FIG. 26B, in the case of the conventional circuit simulator, it is necessary to carefully manually set rise and fall timings of the positive waveform 71 and negative waveform 70. Therefore, the conventional circuit simulator has problems that the above operation is very troublesome and requires a lot of time and it is not easy to perform a random-pattern analysis.